Semiconductor devices such as logic and memory devices are typically fabricated by a sequence of processing steps applied to a substrate or wafer. The various features and multiple structural levels of the semiconductor devices are formed by these processing steps. For example, lithography among others is one semiconductor fabrication process that involves generating a pattern on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield. As design rules and process windows continue to shrink in size, inspection systems are required to capture a wider range of physical defects on wafer surfaces while maintaining high throughput.
One such inspection system illuminates and inspects an unpatterned wafer surface for undesired particles. As semiconductor design rules continue to evolve, the minimum particle size that must be detected by a surface inspection system continues to shrink in size.
Integrated circuit yield loss due to particle contamination from wafer processing equipment must be remediated to realize a cost effective manufacturing process. In a semiconductor fabrication facility, particle contamination levels are monitored by an unpatterned wafer surface inspection system such as the Surfscan® family of products manufactured by KLA-Tencor Corporation, Milpitas, Calif. (USA). A typical contamination metric measured by the inspection tool is the number of particles-per-wafer-pass (PWP). By comparing defect maps measured before and after a test wafer passes through a process tool, the number of added defects is periodically measured and tracked. When PWP exceeds control chart limits, the offending process tool is taken offline to investigate the root cause of the excursion and resolve the problem.
Traditionally, a database of normal and out-of-control defect compositions is generated during the development of the manufacturing processes associated with a particular technology node. During development, scanning electron microscope (SEM) images of added particles are compiled. However, in many cases defect images alone do not positively identify defect types and origins. Thus, in addition, the spectra of characteristic X-rays emitted by particles under electron bombardment are measured with an energy dispersive X-ray (EDX) spectrometer to identify constituent elements.
Subsequently, when excursions occur during high volume manufacturing, an out-of-control test wafer is measured using SEM and EDX tools. The data is compared with the database generated during process development. The measured distribution of defect compositions is compared with the database of past excursions to identify the root cause of the problem. Actions are taken to return the tool to production based on this knowledge.
In general, it is much easier to solve the contamination problem when the chemical composition of the offending particles is known. However, it is a time consuming process to obtain composition measurement results in high volume production environments, where review of patterned wafers by SEM and EDX tools is typically prioritized ahead of review of unpatterned wafers. In addition, review by SEM and EDX tools that are separate from the particle defect review tool requires movement of the wafer from one tool to another, which costs time.
RAMAN spectroscopy is a potential analytical technique that may be employed to identify the composition of particle defects on a wafer surface. U.S. Pat. Nos. 7,777,876 and 9,007,581 issued to Hitachi High-Technologies Corporation describe a surface inspection system that detects both elastic and inelastic scattered light (i.e., Rayleigh and Raman scattering, respectively). A spectrometer is employed to resolve solid-state vibrational modes in the inelastic light, revealing composition information, although it is does not appear to the inventor that any of the reported measurements correspond to Raman spectra from actual particle defects that might be generated by an integrated circuit process tool.
Although atomic vibrational bands of some particles can be observed with laser Raman microspectroscopy, in general, there are many important defect particles of interest (i.e., materials of interest) that do not exhibit active Raman vibrational bands, and are thus unobservable by Raman spectroscopic techniques.
Improvements to scanning surface inspection systems are desired to both detect the presence of defects on the wafer surface and identify the material composition of detected defect particles without transferring the wafer to a different review tool.